Abstract : Monte Carlo techniques were applied in a detailed study of the gamma radiation environment produced in air three feet above fallout uniformly distributed on a smooth ground surface. The basic computations included the energy and angular distributions of the scattered photon flux above monoenergetic plane isotropic gamma-ray sources for ten different source energies from 0.10 to 3.5 Mev. For each source of energy, the flux arriving at the receiver in each of ten energy intervals between 0.04 and 3.5 Mev and eighteen equal receiver angle intervals between 0 (nadir) and 180 degrees (zenith) was calculated. Separate calculations were performed for the uncollided fluxes from the infinite plane isotropic source. The results of the monoenergetic calculations were combined to obtain energy and angular distributions of the photon flux from fallout of four different ages: 1.12 hours, 23.8 hours, 4.57 days, and 9.82 days. Comparisons with measured and previously calculated data, both for actual fallout fields and for simulated infinite plane sources, show favorable agreement. (Author)